1. Field of the Invention
The present invention relates to a vaporizer, and more particularly, to a vaporizer delivery system having multiple containers to provide increased surface area for vaporization of liquids and solid materials, e.g., liquid and solid source reagents used in chemical vapor deposition (CVD), atomic layer chemical vapor deposition (ALCVD) and ion implantation processes.
2. Description of the Related Art
Chemical vapor deposition (CVD) has been extensively used for preparation of films and coatings in semiconductor wafer processing. CVD is a favored deposition process in many respects, for example, because of its ability to provide highly conformal and high quality films, at relatively fast processing times. Further, CVD is beneficial in coating substrates of irregular shapes including the provision of highly conformal films even with respect to deep contacts and other openings.
In general, CVD techniques involve the delivery of gaseous reactants to the surface of a substrate where chemical reactions take place under temperature and pressure conditions that are favorable to the thermodynamics of the desired reaction. The type and composition of the layers that can be formed using CVD is limited by the ability to deliver the reactants or reactant precursors to the surface of the substrate. Various liquid reactants and precursors, are successfully used in CVD applications by delivering the liquid reactants in a carrier gas. In liquid reactant CVD systems, the carrier gas is typically bubbled at a controlled rate through a container of the liquid reactant so as to saturate the carrier gas with liquid reactant and the saturated carrier is then transported to the reaction chamber.
Analogous attempts have been made to deliver solid reactants to a CVD reaction chamber, but with much less success. The delivery of solid precursors in CVD processing is carried out using the sublimator/bubbler method in which the precursor is usually placed in a sublimator/bubbler reservoir which is then heated to the sublimation temperature of the precursor to transform it into a gaseous compound which is transported into the CVD reactor with a carrier gas such as hydrogen, helium, argon, or nitrogen. However, this procedure has been unsuccessful in reliably and reproducibly delivering solid precursor to the reaction chamber for a number of reasons. The major problems with the technique are centered on the inability to consistently vaporize a solid at a controlled rate such that a reproducible flow of vaporized solid precursor can be delivered to the process chamber. Also, it is difficult to ensure complete saturation of the fast flowing carrier gas stream because of a limited amount of exposed surface area of the solid precursor in the vaporizer system and lack of uniform temperature to provide maximum sublimation.
Similar problems are inherent in conventional ion implantation systems that include an ion source in which a dopant element is ionized and then subsequently accelerated to form an ion beam directed at a workpiece surface for implantation. When a solid dopant material is used, it is generally placed within a vaporizer to be heated and the subsequently formed vapors are transported into the interior of the ion source for ionization and subsequent ion beam formation.
Solid ion source material is greatly preferred for safety reasons, however, solid semiconductor dopants have presented serious technical and operating problems. For instance, utilization of a solid precursor material in vaporizers causes extended down time of the instrumentation, poor product quality, and deposit buildup within the vaporizer.
Prior art vaporizer systems have numerous disadvantages, including buildup of condensed material within the vaporizers, and formation of “cold spots” within the interior of the vaporizers due to lack of uniform heating therein. The buildup of unwanted deposits is exacerbated in vaporizer systems that require internal moving surfaces for revolving individual vials and/or wells of source material. These internal mechanisms introduce additional “cold spots” within the vaporizers and provide for further deposition of vaporized material. Additionally, due to the buildup of deposits on internal moving mechanisms, operation of these vaporizers is not efficient or reliable. The shortcomings of the prior art vaporizers are especially noticeable with solid source materials that are temperature-sensitive with a low vapor pressure. Thus, it is difficult to vaporize a solid at a controlled rate such that a reproducible flow of vaporized solid precursor can be delivered to a downstream deposition system.
Accordingly, there is need in the art for a vaporizer system that efficiently vaporizes solid and/or liquid chemical sources without concomitant disadvantages of the prior art, such as thermal disassociation of the source material, inoperability of internal moving parts due to deposit buildup within the vaporizer, condensation of low vapor pressure compounds due to “cold spots” within the vaporizer, and/or inconsistent vapor flow to downstream deposition systems.